1. Field of the Invention
The present invention relates to optical recording media such as an optical disc, an optical-magnetic disc and a phase-change optical disc conforming to ISO standards, and an optical recording apparatus for recording information therein, particularly, it relates to an optical recording medium in which a direct overwrite is possible by the light modulation, and an optical recording apparatus capable of recording information therein by various recording formats including a direct overwrite recording format.
2. Description of Related Art
In a 130 mm optical disc standardized by ISO, a region called a control track is arranged on its inner and outer circumferences (ISO/IEC DIS 10089). In an annular part between 29 and 29.5 mm in radius of the control track on the inner circumferential side, a region called a Phase Encoded Part, hereinafter abbreviated as PEP, and in annular parts between radii 29.52 and 29.7 mm in radius on the inner circumferential side and between 60.15 and 60.5 mm in radius on the outer circumferential side of the control track, standard Format Parts, hereinafter abbreviated as SFP, are provided respectively.
In the PEP, there are no track grooves and, unlike the user's region, information are recorded at low density. This is for reproducing the medium of various characteristics without errors. In the PEP, information for reading the type and SFP of the optical disc are recorded by phase codes. In the PEP, 3 sets, each set consisting of 18 bytes from byte 0 to 17, are recorded in one circuit. In upper 4 bits of the byte 7 of the PEP, a type of the optical disc is recorded, and when the bit 5 is "1" it shows that the optical disc is a postscript type.
The SFP has track grooves, wherein various conditions for recording and reproducing the optical disc are recorded at the same density as the user's region. There are regions of 512 bytes in the SFP altogether, in which reproduced information of the PEP are recorded in the 18 bytes from byte 0 to 17, media information such as recording and reproducing conditions of the optical disc are recorded in the 366 bytes from byte 18 to 383, and system information such as the number of bytes of the user's region are recorded in the 64 bytes from byte 384 to 447. Byte 448 to 511 are reserved as regions for the future standardization or for another standard.
In the region of the SFP where the media information are recorded, respective conditions of the reflectance and the light power with respect to three kinds of laser wavelengths are prescribed.
The light power is prescribed respectively for four kinds of rotational frequency of the disc with respect to the respective wavelengths, so twelve kinds of light power are prescribed altogether. Furthermore, for respective twelve kinds of conditions, a total of nine kinds of light power, three kinds of recording radius and three kinds of pulse width, are prescribed in case of the fixed pulse width process, and a total of four kinds of conditions, the light power and the pulse of three kinds of radius are prescribed in case of the fixed power process, thus a total of 13 kinds of conditions are prescribed. Accordingly, a very large quantity of condition data of the light power of 156 kinds, 13.times.12, are recorded as one byte per one kind.
Similarly, since condition data for erasing are also stored in the media information region of the SFP by the same bytes as for recording, a total of 312 bytes of the condition data in connection with the light power are stored.
Recently, a rewritable optical disc such as an optical-magnetic disc, which can be over-written directly (direct overwritable) with one beam by the light modulation or the magnetic field modulation is proposed. This has been developed to delete the rotation waiting time at erasing the optical-magnetic disc and to speed up the accessing speed. In a magnetic field modulation type, a direction of magnetization is fixed forcibly corresponding to the binary signal as in a magnetic disc apparatus, in which one kind of light power is enough for the recording. On the other hand, in a light modulation type, a plurality of magnetic layers are formed on the optical-magnetic disc, and two kinds of light power are changed corresponding to the binary signal for the recording.
Also the optical disc of phase-change type which can be directly overwritten with one beam by the light modulation similarly using two kinds of light power corresponding to the binary signal is proposed.
FIG. 1(a-c) is a conceptional view of the recording operation of a conventional direct overwrite type optical-magnetic disc.
The optical-magnetic disc (hereinafter referred to as a disc) 1 is composed of a first magnetic layer 22 which has a vertical magnetic anisotropy and whose direction of magnetization is reversible and which is provided on a substrate 21, for example, consisting of glass, and a second magnetic layer 23 which has the vertical magnetic anisotropy and is magnetized in one direction and whose direction of magnetization is not reversible under the same condition as the first magneticlayer 22 and which is provided on the first magnetic layer 22. The second magnetic layer 23 of the disc 1 shown in FIG. 1(b) is magnetized in the opposite direction of the substrate 21 or upwardly.
Next, the operation of overwriting and recording information in the disc 1 will be described.
First, in case of overwriting the information by recording signals PD of "1" and "0" shown in FIG. 1(a) in the disc 1 in which the direction of magnetization of the second magnetic layer 23 is in the opposite direction of the substrate 21 as shown in FIG. 1(b), the disc 1 is rotated and, at the same time, an external magnetic field +H directing downward as shown by the block arrow which is opposite to the magnetization direction of the second magnetic layer 23 thereof is given. Then, while the recording signal is "1", a light beam LB of the high output PH in the projecting direction shown by the white arrow is projected on the first magnetic layer 22 as shown in FIG. 1(c). When the first magnetic layer 22 is heated by the light beam LB and its temperature reaches Curie temperature, the magnetization direction of the first magnetic layer 22 aligns in the same direction as the external magnetic field +H or the direction of the substrate 21, and when the light beam LB is not projected due to the rotation of the disc 1, and the temperature of the first magnetic layer 22 drops, the first magnetic layer 22 is magnetized in the direction of the substrate 21 to record information "1". While recording signal is "0", the light beam LB of the low output PL is projected on the first magnetic layer 22, as shown in FIG. 1(c). Thereby, the coercive force of the first magnetic layer 22 is lowered and aligned in the same direction as the magnetization direction of the second magnetic layer 23, or magnetized in the opposite direction of the substrate 21 to record information "0".
Thereby, no matter what information is recorded before-hand, the direct overwrite is possible.
As such, as for the rewritable optical disc, there are a recording format by which an optical disc is recorded after being erased and a direct overwritable recording format by which it is recorded by two levels of high and low light power.
The optical disc stated above in which the overwrite is possible by the light modulation is still in the development stage and is not standardized by ISO. In case of its standardization, since there are two levels of high and low light power, when it is applied in the aforesaid standard, another combinations of 156 kinds are still necessary, when including the erasing, a total of 468 kinds, 156.times.3, of combinations are necessary. Accordingly, 468 bytes are required as the storing capacity for condition data, and they can not be stored in the media information region of 366 bytes of the ISO standard.
This is true for the optical disc of 90 mm which is now under way of standardization by ISO. Though a region prescribing the light power in the control track is not decided, there is no space to store three kinds of condition data.
As for the rewritable optical disc, since there are two kinds of recording formats as stated above, in the past, it was necessary to record by using the different optical recording apparatus corresponding to the recording format. Accordingly, when the user wants to record by the different recording format, the optical recording apparatus corresponding to the respective recording formats should be prepared.